Several devices are known from the prior art for reducing the drive power requirement of single screw vessels. EP 2 100 808 A1 is mentioned in an exemplary manner here.
In the case of normal single screw vessels, the propeller shaft of the vessel's propeller runs inside the vessel's hull. In the case of these vessels, only the end of the propeller shaft protrudes from the vessel's hull, wherein the ship screw is attached to the protruding end of the propeller shaft. In contrast, several types of vessels are equipped as multi screw vessels, that is, with at least two ship screws or at least two ship propellers, respectively. In particular, twin screw vessels are known, which have two ship screws or ship propellers, respectively. A vessel type, which can often be found in the case of multi screw vessels, is a multi screw vessel with exterior propeller shafts. In the case of this vessel type, the at least two propeller shafts are arranged at least partially outside of the vessel's hull. In the case of this vessel type normally a significant part of the respective propeller shafts is arranged externally. For example, the propeller shaft can also be arranged externally at least 1 m, preferably also at least 3 m, often at a length of 5 m or more. Usually the external section of the propeller shafts is thereby only sheathed by a pipe or the like and is spatially spaced apart from the vessel's hull. Usually each external part of the propeller shafts is supported via a shaft bracket, wherein the shaft bracket is connected to the vessel's hull via shaft bracket arms. The shaft bracket is normally arranged at the end region of the propeller shafts, so that the propeller of the vessel is attached to the propeller shaft in longitudinal direction of the propeller shaft, just behind the shaft bracket. Often each external propeller shaft is supported by means of exactly one shaft bracket.
Devices for improving the energy efficiency or for reducing the drive power requirement, respectively, are not known for such a vessel type of a multi screw vessel with external propeller shafts.